Thermoplastic aliphatic polyester compositions, preparation method and uses thereof

ABSTRACT

The invention concerns thermoplastic aliphatic polyester compositions characterized by a melt flow index (RMFI) ranging between 1.1 and 2.5. The invention also concerns a method for preparing said compositions which are used for making films, foams, flasks or thermoformed products. The resulting films obtained from said compositions are used for making litter bags, films for agricultural use, packaging films, shrouds, diaper drawers and adhesive films.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to compositions for thermoplastic aliphaticpolyesters, a process for their preparation, their use for themanufacture of films, foams, bottles or thermally molded products, thefilms, foams, bottles and thermally molded products obtained and the useof the films obtained.

2. Description of the Background

The thermoplastic aliphatic polyesters, and in particular the_(ε)-caprolactone polymers, have a great many desirable properties,including a good biodegradability and good tensile strength. Theseproperties make the thermoplastic aliphatic polyesters, and inparticular the _(ε)-caprolactone polymers, especially attractive in thepolymer industry.

For many potential applications of the thermoplastic aliphaticpolyesters, and in particular the _(ε)-caprolactone polymers, itnonetheless is necessary that these polymers be characterized by abehavior of hardening under elongation in the molten state. There may becited among these applications the films used, for example, for themaking of trash bags, films for agriculture, films for packaging,shrouds, disposable diapers or adhesive films; foams, bottles andthermally molded products including, for example, pots for young plants.

Unfortunately, the thermoplastic polyesters and in particular the_(ε)-caprolactone polymers, do not naturally display this behavior ofhardening under elongation in the molten state.

It is known to increase the thermoresistance of _(ε)-caprolactonepolymers by bringing about their cross-linking through reaction withorganic peroxides or through radiation with gamma rays. In these cases,however, the polymers obtained are characterized by a very high gellevel (level of insoluble polymers) resulting in the occurrence ofheterogeneous zones in the films which they form and consequently a poorsurface quality of these films. In addition, very often there is noted apuncturing of the bubble which is obtained at the time of blowing,making the obtaining of a film impossible.

In addition, it also is known to add starch to the _(ε)-caprolactonepolymers so that the compositions obtained display the propertiesrequired to give rise to the manufacture of films (C. Bastioli,Macromol. Symp., 135, 193-204 (1998)). Unfortunately, the_(ε)-caprolactone polymers present in these compositions arecharacterized disadvantageously by an excessively low crystallizationspeed, when the external temperature is too high, to ensure a sufficientoutput of the films formed.

SUMMARY OF THE INVENTION

This invention has the purpose of compositions for thermoplasticaliphatic polyesters, in particular for _(ε)-caprolactone polymers,which do not display the aforesaid drawbacks.

This invention also has the purpose of a process for preparation ofthese compositions.

The invention further has the purpose of the use of these compositionsfor the manufacture of films, foams, bottles or thermally moldedproducts as well as the films, foams, bottles and thermally moldedproducts obtained and the use of the films obtained for manufacturingtrash bags, films for agriculture, films for packaging, shrouds,disposable diapers and adhesive films.

To this end, the invention relates first of all to compositions forthermoplastic aliphatic polyesters characterized by an RMFI valueranging between 1.1 and 2.5.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a conical die employed to measure the MFI_(0.3/1) of analiphatic polyester;

FIG. 2 depicts a device for the introduction of an organic peroxide in amixture with carbon dioxide;

FIG. 3 shows the variation in elongational viscosity (kPa·s) of thealiphatic polyester of Examples 1 and 2 at 80° C. versus time for anelongational gradient of 1 s⁻¹;

FIG. 4 shows the variation in dynamic viscosity (Pa·s) of an aliphaticpolyester of Examples 1 and 2 versus a frequency (rad/s) at 80° C.;

FIG. 5 shows the variation in elongational viscosity (kPa·s) of analiphatic polyester of Examples 3 and 4 at 80° C. versus time for anelongational gradient of 1 s⁻¹;

FIG. 6 shows the variation in dynamic viscosity (Pa·s) of an aliphaticpolyester of Examples 3 and 4 versus a frequency (rad/s) at 80° C.;

FIG. 7 shows the variation in elongational viscosity (kPa·s) of analiphatic polyester of Examples 5 and 6 at 80° C. versus time for anelongational gradient of 1 s⁻¹;

FIG. 8 shows the variation in dynamic viscosity (Pa·s) of an aliphaticpolyester of Examples 5 and 6 versus a frequency (rad/s) at 80° C.;

FIG. 9 shows the variation in elongational viscosity (kPa·s) of analiphatic polyester of Examples 7 and 8 at 80° C. versus time for anelongational gradient of 1 s⁻¹; and

FIG. 10 shows the variation in dynamic viscosity (Pa·s) of an aliphaticpolyester of Examples 7 and 8 versus a frequency (rad/s) at 80° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of this invention, RMFI is understood to refer to theratio between two MFI measured at the same temperature, that is, theratio between the MFI_(8/2) obtained with a cylindrical die (height 8 mm+/−0.025, diameter 2.095 mm +/−0.003) and the MFI_(0.3/1) obtained witha conical die as illustrated in FIG. 1. The conical die is characterizedby a cone angle of 60° +/−0.5, an external diameter of 9.48 mm, aninternal diameter of 1.0 mm +/−0.025, a total height of 2.55 mm +/−0.025and a cylindrical-section height of 0.3 mm +/−0.025.

The two MFI are obtained by measuring the quantity of polymer passingthrough a calibrated die, the characteristics of which are set forthhereinabove, under a weight of 5 kg and at the same temperature. Themeasurement temperature generally is 20 to 40° C. higher than themelting temperature of the thermoplastic aliphatic polyester, inparticular 20 to 40° C. higher than the melting temperature of the_(ε)-caprolactone polymers. The measurement temperature preferably is40° C. higher than the melting temperature of the thermoplasticaliphatic polyester, in particular 40° C. higher than the meltingtemperature of the _(ε)-caprolactone polymers. The measurementtemperature usually is 100° C. for the _(ε)-caprolactone homopolymers.The MFI are expressed in dg/min.

The RMFI value is an indication of the branching level in thecompositions according to the invention. An RMFI value ranging between1.1 and 2.5 generally corresponds to a low, but not non-existent,branching level.

The compositions according to the invention usually are characterized byan RMFI value in excess of or equal to 1.1, preferably in excess of orequal to 1.2, particularly preferably in excess of or equal to 1.3

The compositions according to the invention usually are characterized byan RMFI value less than or equal to 2.5, preferably less than or equalto 2, particularly preferably less than or equal to 1.8.

The compositions according to the invention also have a gel level lessthan or equal to 0.5%.

For the purposes of this invention, gel level is understood to refer tothe level of polymers insoluble in chloroform extracted by means of asoxhlet after 8 hours.

The compositions according to the invention usually are characterized bya gel level less than or equal to 0.5%, preferably equal to zero.

The compositions according to the invention also display a hardeningbehavior under elongation in the molten state characterized by anexponential increase in elongational viscosity according to time.

Elongational viscosity is understood to refer to the elongationalviscosity as determined by means of a rheometer, at a temperature 20 to40° C. higher than the melting temperature of the thermoplasticaliphatic polyester, in particular at a temperature 20 to 40° C. higherthan the melting temperature of the _(ε)-caprolactone polymers (thetemperature usually is 80° C. for the _(ε)-caprolactone homopolymers)for an elongation gradient of 1 s⁻¹, on a sample obtained by extrusionand subjected to a release of internal stresses prior to themeasurements.

In addition, the compositions according to the invention arecharacterized in that the point of inflection corresponding to theexponential increase in the elongational viscosity according to timegenerally is less than 3 seconds, preferably less than 2 seconds.

For the purposes of this invention, thermoplastic aliphatic polyestersare understood to refer to aliphatic polyesters and copolyesters inwhich the ester functions are separated by a chain of at least 2 carbonatoms, possibly substituted.

As such polyesters or copolyesters, there may be cited in particularthose derived from hydroxyalcanoates, in particular from3-hydroxybutyrate, from 3-hydroxyvalerate and from 3-hydroxypropionate,but also polybutylene succinate and the _(ε)-caprolactone polymers.

The _(ε)-caprolactone polymers are very particularly preferred.

The thermoplastic aliphatic polyesters of the compositions according tothe invention therefore preferably are _(ε)-caprolactone polymers.

_(ε)-caprolactone polymers are understood to refer to the_(ε)-caprolactone homopolymers as well as to the copolymers with apreponderant _(ε)-caprolactone content, for example at least 50% byweight, with other monomers, preferably with other cyclic lactones.Among these cyclic lactones there may be cited, for example,_(β)-propiolactone, _(γ)-butyrolactone, _(δ)-valerolactone,1,4-dioxane-2-one 1,4-dioxepane-2-one, 1,5-dioxepane-2-one, glycolide(1,4-dioxane-2,5-dione) and the substituted derivatives thereof, as wellas L-lactide, D-lactide, DL-lactide.

The _(ε)-caprolactone polymers preferably are _(ε)-caprolactonehomopolymers.

The compositions for thermoplastic aliphatic polyesters, in particularfor _(ε)-caprolactone polymers, also generally are characterized by anearly linear relationship (absence of a Newtonian plateau) between thedynamic viscosity and the frequency when these are shown on alogarithmic graph.

The dynamic viscosity usually is measured at a temperature 20 to 40° C.higher than the melting temperature of the thermoplastic aliphaticpolyester, in particular at a temperature 20 to 40° C. higher than themelting temperature of the _(ε)-caprolactone polymers (the temperatureusually is 80° C. for the _(ε)-caprolactone homopolymers), between 0.1and 100 rad/s, by means of a rheogoniometer with imposed deformation ona sample with a diameter of 25 mm and a thickness of 2 mm cut into apressed sheet, placed between two parallel plates and subjected to adeformation.

The compositions according to the invention furthermore usually arecharacterized by a tan δ value, at a temperature 20 to 40° C. higherthan the melting temperature of the thermoplastic aliphatic polyester,in particular at a temperature 20 to 40° C. higher than the meltingtemperature of the _(ε) _(ε)-caprolactone polymers (the temperaturegenerally is 80° C. for the _(ε)-caprolactone homopolymers) and 0.1rad/sec, less than or equal to 5, preferably less than or equal to 2.5.

For the purposes of this invention, tan δ is understood to refer to theratio between the modulus of loss G″ and the modulus of elasticity G′,measured at the same temperature 20 to 40° C. higher than the meltingtemperature of the thermoplastic aliphatic polyester, in particular atthe same temperature 20 to 40° C. higher than the melting temperature ofthe _(ε)-caprolactone polymers (the temperature generally is 80° C. forthe _(ε)-caprolactone homopolymers), by means of a rheogoniometer withimposed deformation on a sample, placed between two parallel plates andsubjected to a deformation, with a diameter of 25 mm and a thickness of2 mm, cut into a pressed sheet.

The compositions according to the invention furthermore usually arecharacterized by a more rapid crystallization than the correspondingcompositions characterized by an RMFI value ranging between 0.85 and1.05.

Thus, the compositions according to the invention usually have acrystallization temperature, measured by differential thermal analysis,in the first cooling pass, after having erased the thermal historythereof, with a scanning speed of 10° K/min, at least 1° C. higher thanthat of corresponding compositions characterized by an RMFI valueranging between 0.85 and 1.05.

For the purposes of this invention, corresponding compositionscharacterized by an RMFI value ranging between 0.85 and 1.05 areunderstood to refer to compositions corresponding from any point of viewto the compositions according to the invention, but which arecharacterized by an RMFI value ranging between 0.85 and 1.05. Such anRMFI value ranging between 0.85 and 1.05 generally corresponds to anon-existent branching level.

Alternatively, the kinetics of crystallization may be revealed bymeasurements of dynamic viscosity according to time, for a givendeformation frequency and thermal treatment. The compositions accordingto the invention thus have a crystallization speed such that the ratiobetween this crystallization speed and the crystallization speed ofcorresponding compositions characterized by an RMFI value rangingbetween 0.85 and 1.05, measured at the same temperature, is in excess of1.

For the purposes of this invention, crystallization speed is understoodto refer to the speed at which the crystals grow in the compositionsaccording to the invention.

The crystallization speed may be determined by means of a rheogoniometerwith imposed deformation. Measurements of the dynamic viscosityaccording to time, for a given deformation frequency, are performed on asample subjected to a specific thermal treatment so as to follow thedevelopment of this rheological property throughout the crystallizationprocess. The slope of the curve seen when the dynamic viscosityincreases at the time of crystallization is a measurement of thecrystallization speed.

The compositions according to the invention preferably have acrystallization speed such that the ratio between this crystallizationspeed and the crystallization speed of corresponding compositionscharacterized by an RMFI value ranging between 0.85 and 1.05, measuredat the same temperature, is in excess of 1.25, particularly preferablyin excess of 1.5.

The compositions according to the invention also have an induction timefor crystallization such that the ratio between this induction time andthe induction time of corresponding compositions characterized by anRMFI value ranging between 0.85 and 1.05, measured at the sametemperature, is less than 1.

For the purposes of this invention, induction time for crystallizationis understood to refer to the time required for nucleation to occur inthe compositions according to the invention.

The induction time for crystallization corresponds to a time duringwhich the dynamic viscosity remains constant prior to increasingsignificantly at the time of the measurements of dynamic viscosityaccording to time explained hereinabove.

The compositions according to the invention preferably have an inductiontime for crystallization such that the ratio between this induction timeand the induction time of corresponding compositions characterized by anRMFI value ranging between 0.85 and 1.05, measured at the sametemperature, is less than 0.85, particularly preferably less than 0.7.

The compositions according to the invention preferably comprise athermoplastic aliphatic polyester, in particular an _(ε)-caprolactonepolymer, the mean molecular mass in number of which, measured by gelpermeation chromatography, is in excess of or equal to 10,000 g/mole.

The mean molecular mass in number of the thermoplastic aliphaticpolyester, in particular of the _(ε)-caprolactone polymer, is preferablyin excess of or equal to 10,000, particularly preferably in excess of orequal to 25,000, very particularly preferably in excess of or equal to40,000 g/mole.

The compositions according to the invention preferably comprise athermoplastic aliphatic polyester, in particular an _(ε)-caprolactonepolymer, the mean molecular mass in number of which, measured by gelpermeation chromatography, is less than or equal to 200,000 g/mole.

The mean molecular mass in number of the thermoplastic aliphaticpolyester, in particular of the _(ε)-caprolactone polymer, is preferablyless than or equal to 200,000, particularly preferably less than orequal to 175,000, very particularly preferably less than or equal to150,000 g/mole.

Mean molecular mass in number measured by gel permeation chromatographyis understood to refer to the mean molecular mass in number measured bygel permeation chromatography, by means of a column of the PolymerLaboratories Mix-C type and a refractometer of the Waters DifferentialRefractometer R401 type. The concentration of the sample is 20 mg/mL andthe flow rate is 1 mL/min. The standards used are polystyrene standards.In the specific case of the _(ε)-caprolactone polymers, the solvent usedis chloroform and the conversion factor used is 0.6.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of the compositions according to theinvention generally consists of a single polymer.

The thermoplastic aliphatic polyester of the compositions according tothe invention also may result from the mixing of at least twothermoplastic aliphatic polyesters. In particular, the _(ε)-caprolactonepolymer of the compositions according to the invention also may resultfrom the mixing of at least two _(ε)-caprolactone polymers.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, may result from the mixing of at least twothermoplastic aliphatic polyesters, in particular of at least two_(ε)-caprolactone polymers, with mean molecular masses in number whichare different but such that the thermoplastic aliphatic polyester, inparticular the _(ε)-caprolactone polymer, of the compositions accordingto the invention is characterized by a mean molecular mass in number asdefined hereinabove.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of the compositions according to theinvention preferably results from the mixing of 0.1 to 99.9% by weightof the total quantity of polymers, of a thermoplastic aliphaticpolyester, in particular of an _(ε)-caprolactone polymer, of lowmolecular mass, and of 99.9 to 0.1% by weight of the total quantity ofpolymers, of a thermoplastic aliphatic polyester, in particular of an_(ε)-caprolactone polymer, of high molecular mass.

In a particularly preferred manner, the thermoplastic aliphaticpolyester, in particular the _(ε)-caprolactone polymer, of thecompositions according to the invention results from the mixing of 0.1to 80% by weight of the total quantity of polymers, of a thermoplasticaliphatic polyester, in particular of an _(ε)-caprolactone polymer, oflow molecular mass, and of 99.9 to 20% by weight of the total quantityof polymers, of a thermoplastic aliphatic polyester, in particular of an_(ε)-caprolactone polymer, of high molecular mass.

In a very particularly preferred manner, the thermoplastic aliphaticpolyester, in particular the _(ε)-caprolactone polymer, of thecompositions according to the invention results from the mixing of 0.1to 70% by weight of the total quantity of polymers, of a thermoplasticaliphatic polyester, in particular of an _(ε)-caprolactone polymer, oflow molecular mass, and of 99.9 to 30% by weight of the total quantityof polymers, of a thermoplastic aliphatic polyester, in particular of an_(ε)-caprolactone polymer, of high molecular mass.

In a truly preferred manner, the thermoplastic aliphatic polyester, inparticular the _(ε)-caprolactone polymer, of the compositions accordingto the invention results from the mixing of 10 to 60% by weight of thetotal quantity of polymers, of a thermoplastic aliphatic polyester, inparticular of an _(ε)-caprolactone polymer, of low molecular mass, andof 90 to 40% by weight of the total quantity of polymers, of athermoplastic aliphatic polyester, in particular of an _(ε)-caprolactonepolymer, of high molecular mass.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of low molecular mass usually has a meanmolecular mass in number, measured by gel permeation chromatography, inexcess of or equal to 10,000 g/mole and less than or equal to 60,000g/mole, and the thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of high molecular mass usually has a meanmolecular mass in number, measured by gel permeation chromatography, inexcess of 60,000 g/ mole and less than or equal to 200,000 g/mole.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of low molecular mass usually has a meanmolecular mass in number, measured by gel permeation chromatography,less than or equal to 60,000 g/mole.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of low molecular mass usually has a meanmolecular mass in number, measured by gel permeation chromatography, inexcess of or equal to 10,000, preferably in excess of or equal to25,000, particularly preferably in excess of or equal to 40,000 g/mole.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of high molecular mass usually has a meanmolecular mass in number, measured by gel permeation chromatography, inexcess of 60,000 g/mole.

The thermoplastic aliphatic polyester, in particular the_(ε)-caprolactone polymer, of high molecular mass usually has a meanmolecular mass in number measured by gel permeation chromatography lessthan or equal to 200,000, preferably less than or equal to 175,000,particularly preferably less than or equal to 150,000 g/mole.

The compositions according to the invention furthermore may comprise acertain quantity of other biodegradable polymers such as, for example,polylactic acid, native or thermoplastic starch and modified orunmodified cellulose.

The compositions according to the invention furthermore may comprise oneor more common additives for thermoplastic aliphatic polyesters, inparticular for _(ε)-caprolactone polymers, such as, for example,stabilizing agents, antioxidant additives, antistatic agents, organic orinorganic coloring agents, antiblocking agents, nucleant agents andfiller materials, etc.

The compositions according to the invention preferably furthermorecomprise at least one filler material.

Any customary filler material for thermoplastic aliphatic polyesters, inparticular for _(ε)-caprolactone polymers, may be used. Among the latterthere may be cited, for example, neutral or basic carbon blacks, metaloxides (in particular iron oxide), silica, kaolin, mica, talc, zeolites,fiberglass, natural fibers (flax, wood, sisal), biodegradable fillermaterials (recycled paper, native starch) and calcium carbonate. Thefiller materials also may be surface-treated in order to facilitatetheir dispersion in the compositions according to the invention.

A particularly preferred filler material is calcium carbonate.

The compositions according to the invention usually comprise up to 80%by weight, preferably up to 60% by weight, particularly preferably up to50% by weight, very particularly preferably up to 40% by weight of atleast one filler material.

The compositions according to the invention also comprise at least onestabilizing agent.

All the stabilizing agents for thermoplastic aliphatic polyesters, inparticular for _(ε)-caprolactone polymers, may be used. Particularlypreferred stabilizing agents are compounds comprising a stericallycongested phenol group, phosphorous compounds and mixtures thereof. Itis a matter, for example, of compounds such as1,3,5-trimethyl-2,4,6-tris(3,5-t-butyl-4-hydroxybenzyl)benzene,pentaerythrityl tetrakis-(3,5-di-t-butyl4-hydroxyphenylpropionate),tris-(2,4-di-t-butylphenyl)phosphite or the mixture of pentaerythrityltetrakis-(3, 5-di-t-butyl4-hydroxyphenylpropionate) andtris-(2,4-di-t-butylphenyl)phosphite, preferably in equal quantities. Astabilizing agent which is well suited is1,3,5-trimethyl-2,4,6-tris(3,5-t-butyl-4-hydroxybenzyl)benzene.

The compositions according to the invention may be obtained by anyprocess whatsoever. Good results are obtained if they are prepared bymeans of the process according to the invention.

The invention also relates to a process for preparation of compositionsfor thermoplastic aliphatic polyesters according to which there iscaused to react in a molten mass in an extruder a thermoplasticaliphatic polyester with a radical generator in a quantity rangingbetween 0.01 and 0.2% by weight in relation to the thermoplasticaliphatic polyester.

The thermoplastic aliphatic polyesters are defined hereinabove andpreferably are _(ε)-caprolactone polymers.

In general the radical generator is used in the process according to theinvention in a quantity sufficient to permit reaction between theradical generator and the thermoplastic aliphatic polyester, inparticular the _(ε)-caprolactone polymer. In addition, it is desirablethat the quantity not exceed the necessary quantity, because any excessof radical generator can lead to a cross-linking of the polymerspresent.

In general the quantity of radical generator ranges between 0.01 and0.2% by weight in relation to the thermoplastic aliphatic polyester, inparticular in relation to the _(ε)-caprolactone polymer.

The quantity is usually at least equal to 0.01, preferably at leastequal to 0.025, particularly preferably at least 0.05% by weight inrelation to the thermoplastic aliphatic polyester, in particular inrelation to the _(ε)-caprolactone polymer. In general, the quantity isat most 0.2, preferably it is at most 0.15, particularly preferably itis at most 0.125% by weight in relation to the thermoplastic aliphaticpolyester, particularly in relation to the _(ε)-caprolactone polymer.

As a radical generator, there preferably is used an organic peroxide,and more particularly an alkylperoxide. Among the latter there may bementioned t-butylcumyl peroxide,1,3-di(2-t-butylperoxyisopropyl)benzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(t-butyl)peroxide and2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne. The2,5-dimethyl-2,5-di-t-butylperoxy-hexane (DHBP) is particularlypreferred.

The radical generator may be introduced in any manner whatsoever so longas it is introduced continuously over time and is well dispersed in themolten material. Thus, for example, the radical generator may beintroduced by spraying, for example by means of a spray-type injector ora vaporizer.

The radical generator preferably is introduced into the extruder in amixture with carbon dioxide, by means of a thermoplastic aliphaticpolyester containing it or by means of a filler material containing it.

According to a first preferred embodiment of the invention, the radicalgenerator is introduced into the extruder in a mixture with carbondioxide. Any device permitting the mixing of the radical generator andthe carbon dioxide and the introduction of this mixture into theextruder may be used for this purpose. Depending on the temperature andpressure conditions, the carbon dioxide may be in the liquid, gaseous orsupercritical state.

According to a second preferred embodiment of the invention, the radicalgenerator is introduced into the extruder by means of a thermoplasticaliphatic polyester, preferably an _(ε)-caprolactone polymer, containingthe radical generator.

According to a first variant, the radical generator, preferably DHBP, isintroduced into the extruder in the form of a mixture of a thermoplasticaliphatic polyester, preferably an _(ε)-caprolactone polymer, in thesolid state with the radical generator, preferably DHBP, also in thesolid state. In a particularly preferred manner, the _(ε)-caprolactonepolymer exists in the form of a powder the particles of which are of asize less than or equal to 100 μm. In a particularly preferred manner,the DHBP exists in the form of a talc powder impregnated with DHBP.

According to a second variant, the radical generator, preferably DHBP,is introduced into the extruder by means of a thermoplastic aliphaticpolyester, preferably an _(ε)-caprolactone polymer, impregnated inadvance with the radical generator, preferably DHBP, at the time of apretreatment.

According to a third preferred embodiment of the invention, the radicalgenerator is introduced into the extruder by means of a filler materialcontaining the radical generator. In a particularly preferred manner,the DHBP is introduced in the form of a mixture of calcium carbonate inthe solid state and DHBP in the solid state, for example in the form ofa talc powder impregnated with DHBP.

For the purposes of this invention, reaction in a molten mass isunderstood to refer to any reaction in the substantial absence ofsolvent or of diluent and at a temperature at least equal to the meltingtemperature of the thermoplastic aliphatic polyesters, in particular the_(ε)-caprolactone polymers.

Extruder is understood to refer to any continuous device comprising atleast one loading zone and, at its outlet, a discharge zone preceded bya compression zone, the latter forcing the molten mass to pass throughthe discharge zone. In addition, the discharge zone may be followed by agranulation device or a device imparting a shaped form, such as a filmor a bottle paraison, to the extruded material. Advantageously use willbe made of known extruders based on twin-screw operation, whether co- orcounter-rotary.

The extruder used in the process according to this invention preferablyis fitted out so that it comprises successively a loading zone, amelting zone for the material, a homogenization zone, a reaction zone,optionally a zone for introduction of additives, optionally a degassingzone and a discharge zone preceded by a compression zone. Each of thesezones has a very specific function and is at a very specifictemperature.

The loading zone has the function of providing for loading of thepolymer or polymers. It usually is at a temperature less than or equalto 20° C.

The zone for melting of the material has the function of providing forthe melting of the material.

The homogenization zone has the function of homogenizing the moltenmaterial.

The reaction zone has the function of providing for reaction.

The temperature in the zone for melting and in the zone forhomogenization of the material usually is in excess of or equal to themelting temperature of the polymer and less than or equal to thetemperature at which the half-life period of the radical generator isten times greater than the dwell time of the material in the zone.

The temperature in the reaction zone usually is in excess of or equal tothe temperature at which the half-life period of the radical generatoris less than or equal to the dwell time of the material in this zone.

The zone for introduction of additives has the function of providing forthe introduction of additives at the time when the latter are added. Thetemperature of this zone usually is the same as that of the reactionzone or is slightly higher.

The degassing zone has the function of permitting elimination of thevolatile products of decomposition of the radical generator. Thetemperature of this zone usually is the same at that of the reactionzone or is slightly lower.

The compression zone has the function of compressing the material so asto force it through the discharge zone. The temperature in thecompression zone usually is dependent on the viscosity of the materialto be discharged.

The discharge zone has the function of providing for the discharge ofthe material. The temperature in the discharge zone usually is dependenton the viscosity of the material to be discharged.

When the radical generator is introduced into the extruder in a mixturewith carbon dioxide, it preferably is introduced into thematerial-melting zone of the extruder.

When the radical generator is introduced into the extruder by means of athermoplastic aliphatic polyester, in particular an _(ε)-caprolactonepolymer, it preferably is introduced into the loading zone of theextruder.

When the radical generator is introduced into the extruder by means of afiller material containing the radical generator, it preferably isintroduced into the loading zone of the extruder.

In the course of the process, there may be incorporated at any pointwhatsoever one or more common additives for thermoplastic aliphaticpolyesters, in particular _(ε)-caprolactone polymers, such as thosedescribed hereinabove.

In a preferred form of the process, at least one filler material isadded during the process.

The preferred filler materials are those described hereinabove. A veryparticularly preferred filler material is calcium carbonate.

In the process according to the invention, there usually is added up to80% by weight, preferably up to 60% by weight, particularly preferablyup to 50% by weight, very particularly preferably up to 40% by weight ofat least one filler material.

In the process according to the invention, there also may be added, forexample, at least one stabilizing agent.

The preferred stabilizing agents are those described hereinabove. Astabilizing agent which is well suited is1,3,5-trimethyl-2,4,6-tris(3,5-t-butyl-4-hydroxybenzyl)benzene.

When a stabilizing agent is added, it preferably is done at the sametime as the filler material. These then preferably are introduced intothe additive introduction zone.

The invention further relates to compositions for thermoplasticaliphatic polyesters, in particular _(ε)-caprolactone polymers, derivingfrom the process according to the invention.

This invention also relates to the use of the compositions according tothe invention for the manufacture of films, foams, bottles or thermallymolded products.

The invention also relates to the films obtained starting from thecompositions according to the invention. The films obtained preferablyare produced by blowing extrusion.

The invention also relates to the use of the films obtained for themanufacture of trash bags, films for agriculture, films for packaging,shrouds, disposable diapers and adhesive films.

The invention also relates to the foams obtained starting from thecompositions according to the invention.

The invention also relates to the bottles obtained starting from thecompositions according to the invention.

The invention also relates to the thermally molded products obtainedstarting from the compositions according to the invention.

The compositions for thermoplastic aliphatic polyesters, in particular_(ε)-caprolactone polymers, according to the invention thereforeadvantageously are characterized by a rheological behavior (elongationalviscosity, tan δ, dynamic viscosity) such that they are characterized byan increase in deformation resistance at the time of blowing, hence anextremely stable blowing process and the formation of extremely stablebubbles with a homogeneous thickness.

In addition, the compositions according to the invention arecharacterized by a very low, or even non-existent, gel level (level ofinsoluble polymers), giving rise to films having no or very fewheterogeneous zones and consequently displaying a very good surfacequality and a transparency suited to the contemplated applications.

In addition, the compositions according to the invention arecharacterized by a greater crystallization speed than the correspondingcompositions according to the prior art. By virtue thereof, theproduction yield of the films made is less sensitive to cooling and tothe ambient temperature.

The films, foams, bottles or thermally molded products obtained startingfrom the compositions according to the invention furthermore arebiodegradable, Finally, the films obtained also are characterized by avery good printability.

The examples which follow serve to illustrate this invention, withoutthereby limiting the scope thereof.

Poly-_(ε)-caprolactones

The poly-_(ε)-caprolactones used are the commercialpoly-_(ε)-caprolactones CAPA® 650 and CAPA® 680 sold by SOLVAY INTEROX.They are characterized by:

A mean molecular mass in number of 44,000 g/mole for the CAPA® 650poly-_(ε)-caprolactones and 70,000 g/mole for the CAPA® 680poly-_(ε)-caprolactone. The mean molecular mass in number is measured bygel permeation chromatography, using chloroform as solvent, by means ofa column of the Polymer Laboratories Mix-C type and a refractometer ofthe Waters Differential Refractometer R401 type. The concentration ofthe sample is 20 mg/mL and the flow rate is 1 mL/min. The standards usedare polystyrene standards and the conversion factor used is 0.6.

A melting temperature of 58-60° C. for the CAPA® 650poly-_(ε)-caprolactones and for the CAPA® 680 poly-_(ε)-caprolactone.The melting temperature is measured by differential thermal analysis, inthe second pass and with a scanning speed of 10° K/min.

The CAPA® 65100 poly-_(ε)-caprolactone sold by SOLVAY INTEROX also wasused. This poly _(ε)-caprolactone is chemically identical to the CAPA®650 poly-_(ε)-caprolactone but is supplied in the form of a powder theparticles of which are of a size less than or equal to 100 μm.

Radical Generator

The radical generator used is 2,5-dimethyl-2,5-di-t-butylperoxyhexane(DHBP) sold under the brand name LUPERSOL® 101 by PEROXID CHEMIE or2,5-dimethyl-2, 5-di-t-butylperoxyhexane (DHBP) absorbed on talc, soldunder the name DHBP-45-IC by PEROXID CHEMIE.

Filler Material

The filler material, when it is used, is calcium carbonate sold underthe brand name OMYA BLH™ by OMYA Benelux.

Stabilizing Agent

The stabilizing agent, when it is used, is1,3,5-trimethyl-2,4,6-tris(3,5-t-butyl-4-hydroxybenzyl)benzene soldunder the brand name IRGANOX® 1330 by CIBA.

Extruders

A first extruder used is the twin-screw co-rotary WERNER & PFLEIDERERZSK® 40 extruder. The diameter of the screws is 40 mm and their lengthis 1360 mm. The rotation speed of the screws is 200 rpm (rotations perminute).

The extruder is fitted out so that it comprises successively a loadingzone, a zone for melting of the material, a homogenization zone, areaction zone, optionally a zone for introduction of additives and adischarge zone preceded by a compression zone. Each of these zones is ata very specific temperature.

The _(ε)-caprolactone polymer loading zone is at a temperature less thanor equal to 20° C.

The zone for melting of the material is at a temperature of 130° C. TheDHBP is introduced into this zone in a mixture with carbon dioxide bymeans of the introduction device described hereinbelow.

The homogenization zone is at a temperature of 130° C.

The reaction zone is at a temperature of 180° C.

The zone for introduction of additives (filler material and stabilizingagent), when they are added, is at a temperature of 180° C.

The compression zone is at a temperature of 180° C.

The discharge zone is at a temperature of 180° C.

A second extruder used is the twin-screw co-rotary WERNER & PFLEIDERERZSK® 58 extruder. The diameter of the screws is 58 mm and their lengthis 2160 mm. The rotation speed of the screws is 200 rpm (rotations perminute).

The extruder is fitted out so that it comprises successively a loadingzone, a zone for melting of the material, a homogenization zone, areaction zone, optionally a zone for introduction of additives and acompression-discharge zone preceded by a degassing zone. Each of thesezones is at a very specific temperature.

The _(ε)-caprolactone polymer loading zone is at a temperature less thanor equal to 20° C. The DHBP is introduced into this zone in the form ofa mixture with an _(ε)-caprolactone polymer.

The zone for melting of the material is at a temperature of 120° C.

The homogenization zone is at a temperature of 120° C.

The reaction zone is at a temperature of 180° C.

The degassing zone is at a temperature of 160° C.

The compression-discharge zone is at a temperature of 120° C.

Device for Introduction of LUPERSOL® 101 DHBP in a Mixture with CarbonDioxide

The device for introduction of organic peroxide in a mixture with carbondioxide is illustrated schematically in FIG. 2.

The LUPERSOL® 101 DHBP contained in tank 6 is fed into mixing chamber 2by means of pump 1. The liquid carbon dioxide contained in tank 4 iscooled to −10° C. in cryothermostat 3 prior to being fed into the mixingchamber 2 by means of a pump 1′. The mixture of DHBP and liquid carbondioxide prepared in the mixing chamber then is discharged into injector7 the pressure of which is read by means of a pressure sensor 5.

Liquid carbon dioxide tank 4 is a carboy under pressure with carbondioxide.

Pumps 1 and 1′ are pumps of the GILSON 305 or 306 type. The head of pump1′ provided for the carbon dioxide is equipped with a GILSON 5/10/25SGthermostat kit which makes it possible to cool the head to −10° C. Thecoolant liquid is isopropanol cooled in a JUBALO F30 typecryothermostat.

This same cryothermostat is used to cool the liquid carbon dioxide(cryothermostat 3).

Mixing chamber 2 is an analytical mixer equipped with a GILSON 811C typehelix.

Injector 7 is an injector making it possible to work under high pressure(in excess of 74 bar).

A pressure sensor 5 of the GILSON 806 type is placed between pump 1′ andmixing chamber 2 to read the pressure in the injector (between 90 and120 bar).

The injector of the introduction device is arranged perpendicularly tothe cover of the extruder and opens tangentially onto the thread of theextrusion screw. It is arranged precisely perpendicularly to the meltingzone of the extruder. The carbon dioxide at the injector generally is inthe supercritcal state.

Preparation of the Mixture of DHBP45-IC with CAPA® 65100Poly-_(ε)-caprolactone

The 2,5-dimethyl-2,5-di-t-butylperoxyhexane DHBP-45-IC was mixed withCAPA® 65100 poly-_(ε)-caprolactone in a mixer stirred at slow speed, inthe ratio of 30 g of DHBP-45-IC per kg of CAPA® 65100poly-_(ε)-caprolactone.

Characterization of the Compositions Obtained

The compositions obtained are characterized by:

MFI measurements for determination of the RMFI,

measurement of the gel level,

measurement of the mean molecular mass in number,

measurement of their crystallization temperature,

measurements of dynamic rheometry (ARES) for determination of thecrystallization speed and the induction time on the one hand, and fordetermination of the viscoelastic properties (dynamic viscosity, tan δ)according to frequency, on the other hand,

measurements of elongational rheometry (RME) for determination of theelongational viscosity.

Determination of the RMFI

The RMFI is obtained by calculating the ratio between the MFI_(8/2)obtained with a cylindrical die (height 8 mm +/−0.025, diameter 2.095 mm+/−0.003) and the MFI_(0.3/1) obtained with a conical die such asillustrated in FIG. 1. The conical die is characterized by a cone angleof 60° +/−0.5, an external diameter of 9.48 mm, an internal diameter of1.0+/−0.025, a total height of 2.55 mm +/−0.025 and a cylindricalsection height of 0.3 mm +/−0.025. The two MFI are obtained by measuringthe quantity of polymer passing through a calibrated die, thecharacteristics of which are set forth hereinabove, at a temperature of100° C. under the action of a mass of 5 kg and at the same temperature.The MFI are expressed in dg/min.

Measurement of the Gel Level

The gel level is the level of polymers insoluble in chloroform extractedby means of a soxhlet after 8 hours.

Measurement of the Mean Molecular Mass in Number

The mean molecular mass in number is measured by gel permeationchromatography, using chloroform as solvent, by means of a column of thePolymer Laboratories Mix-C type and a refractometer of the WatersDifferential Refractometer R401 type. The concentration of the sample is20 mg/mL and the flow rate 1 mL/min. The standards used are polystyrenestandards and the conversion factor used is 0.6.

Measurement of the Crystallization Temperature

The crystallization temperature of the compositions is measured bydifferential thermal analysis, in the first cooling pass, after havingerased the thermal history thereof and with a scanning speed of 10K/min.

Thus the sample, after having been maintained at −50° C. for 5 minutes,is brought to a temperature of 120° C. with a constant sweeping speed of10° K/min. After having been maintained for 5 minutes at 120° C., thesample is subjected to a cooling with a scanning speed of 10° K/min. andit is at the time of this cooling that the crystallization temperatureis measured.

Measurements of Dynamic Rheometry

The measurements of dynamic rheometry are performed by means of arheogoniometer with imposed deformation, marketed by RHEOMETRICS underthe name ADVANCED RHEOLOGICAL EXPANSION SYSTEM (ARES). The measurementsare performed on the sample, placed between 2 parallel plates andsubjected to a periodic deformation applied by the movement of one platewith respect to the other, with a diameter of 25 mm and a thickness of 2mm cut into a pressed sheet.

For the determination of the crystallization speed and the inductiontime, the sample is subjected to a thermal treatment calculated so as tofollow the evolution of the dynamic viscosity, at a specific deformationfrequency, according to time, throughout the crystallization process.The thermal treatment consists in heating the sample to 150° C. with aspeed of 24° C./min, maintaining it at 150° C. for 10 minutes, coolingit to 47° C. with a speed of 24° C./min and then to 45° C. with a speedof 2° C./min. The evolution of the dynamic viscosity at 45° C.,according to time, at a frequency of 1 rad/s, is entered on a graph.

The slope of the curve seen when the dynamic viscosity increases at thetime of crystallization is a measurement of the crystallization speed.

The induction time for the crystallization corresponds to the timeduring which the dynamic viscosity remains constant prior to increasingsignificantly at the time of nucleation in the _(ε)-caprolactonepolymers, zero time corresponding to arrival at the temperature of 45°C.

For determination of the viscoelastic properties (dynamic viscosity, tanδ) according to frequency, the sample is subjected to a deformation at aconstant temperature of 80° C. The result of the measurement (ARESdiagram) is expressed by the variation, at 80° C., of the dynamicviscosity expressed in Pa.s or the moduli G″ (modulus of loss) and G′(modulus of elasticity), expressed in Pa, according to the frequencyexpressed in rad/s. Tan δ is the ratio between the moduli G″ and G′.

Measurements of Elongational Rheometry

The measurements of elongational rheometry are performed by means of arheometer marketed by RHEOMETRICS under the name RME (RHEOMETRICSELONGATIONAL RHEOMETER FOR MELTS). The sample (52×7×1.5 mm) is obtainedby extrusion and is subjected to a procedure for release of the internalstresses prior to the measurements.

The result of the measurement (RME diagram) is expressed by thevariation, at 80° C., of the elongational viscosity in the molten state(expressed in kPa.s) according to time (expressed in s) for anelongation gradient (expressed in s⁻¹) of 1.

Films

Films were made by blowing extrusion starting from the compositionsobtained, when that was possible, by means of an extruder of the DOLCI20 type. This single-screw extruder is used to bring the material to themolten state (75-150° C.) prior to forcing it through a ring-shaped diewith a diameter of 30 mm and an air-gap of 0.75 mm (core of 28.5 mm),positioned perpendicularly to the axis of the extruder, so that theproduct exits vertically upward. The flow rate of the material isregulated by changing the speed of rotation of the screw. The tubularparaison then is inflated by an internal air pressure and cooledexternally by a flow of air distributed uniformly around the bubble thusformed a few centimeters above the die. The air may be refrigerated, butit advantageously is at ambient temperature. The rate of inflation(defined as equal to the ratio of the perimeter of the film over theperimeter of the die) is regulated by adjusting the internal airpressure. The bubble then is flattened gradually by 2 guides, thengripped between 2 rollers, of which at least one is coated with rubberand at least one is driven. The tubular paraison therefore also is drawnin the axial direction by the two gripping rollers. The rate of drawing(defined as equal to the ratio of the speed of the film at winding overthe speed of the film at the die) is adjusted by varying the speed ofthe gripping rollers. The final thickness of the film depends on theair-gap of the die, the rate of inflation and the rate of drawing.

Characterization of the Films Obtained

Measurements of traction, impact resistance and tear resistance wereperformed on the films obtained.

Measurements of Traction

The measurements of traction are effected in accordance with ISOstandard 527-3 (1993) on test-pieces 50×15 mm², at 23° C. and 50%relative humidity and with a speed of 100 mm/min (INSTRON tractivemachine).

The nominal stress (ratio of the tractive force over the initialsection) and the elongation (ratio of the length after traction over theinitial length, or 50 mm) in the direction of extrusion or in thedirection perpendicular to extrusion are determined.

The nominal stress is expressed in MPa and the elongation in %.

Measurements of Impact Resistance

The impact resistance is measured according to ISO standard 7765-1(1998) (method A). The ratio of the weight thus determined to thethickness of the sample is calculated to express the result in g/μm.

Measurement of Resistance to Tear Propagation

The resistance to tear propagation is measured according to the“Elmendorf” technique described in the ASTM-D1922 standard ontest-pieces with a constant radius, at 23° C. and 50% relative humiditywith a 1.6 kgf pendulum. In the case of films having a low tearresistance, several samples were superposed as the standard specifies.To prevent them from becoming fused at the time of impact, the differentlayers then were separated with a very thin insert, for which it wasverified that it would not disrupt the measurement.

The resistance to tear propagation is determined in the direction ofextrusion or in the direction perpendicular to extrusion.

The resistance to tear propagation is expressed in N.

EXAMPLE 1

The CAPA® 680 poly-_(ε)-caprolactone was introduced into the loadingzone of the WERNER & PFLEIDERER ZSK® 40 extruder with a flow rate of 30kg/h and was spread through the different zones of the extruder.

In the melting zone of the extruder, the LUPERSOL® 101 DHBP, in amixture with carbon dioxide, was sprayed onto the poly-_(ε)-caprolactoneby means of the introduction device described hereinabove. The LUPERSOL®101 DHBP was introduced at the rate of 1 g per kg of CAPA® 680poly-_(ε)-caprolactone and at the rate of 570 μl of DHBP in 5 mL ofcarbon dioxide per minute.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 3 (symbol _(∘)).

The variation in dynamic viscosity (expressed in Pa.s) according to thefrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 4(symbol _(∘)).

Two films (No. 1.1, 1.2) were prepared starting from the compositionaccording to example 1 in the manner described hereinabove and with theconditions set forth hereinbelow.

Flow rate Speed, Drawing Inflation Film No. kg/h m/minimum Thicknessrate rate 1.1 2.3 1.7 48 3 4.4 1.2 2.3 3.5 19 6.3 4.4

The two films are characterized by an impact resistance of 1.2 and 2.3g/μm respectively. Film No. 1.1 is characterized by a resistance to tearpropagation of 0.3 N in the direction of extrusion and of 0.65 N in thedirection perpendicular to extrusion.

EXAMPLE 2 (COMPARATIVE)

Example 1 was repeated in the absence of DHBP.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 3 (symbol _(∘)).

The variation in dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 4(symbol _(∘)).

It was not possible to obtain a film by blowing extrusion from thecomposition according to example 2.

EXAMPLE 3

Example 1 was repeated, replacing the CAPA® 680 poly-_(ε)-caprolactonewith a mixture of 40% by weight of CAPA® 680 poly-_(ε)-caprolactone and60% by weight of CAPA® 650 poly-_(ε)-caprolactone. The mean molecularmass in number, measured by gel permeation chromatography, is 55,000g/mole.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 5 (symbol _(□)).

The variation in dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 6(symbol _(□)).

A film was prepared starting from the composition according to example 3in the manner described hereinabove and with the conditions set forthhereinbelow.

Flow rate Speed, Drawing Inflation Film No. kg/h m/minimum Thicknessrate rate 3.1 2.1 1.3 59 2.5 4.5

The measurements of traction performed on this film yield the followingresults: the nominal stress in the direction of extrusion is 46 MPa, theelongation in the direction of extrusion is 1000%, the nominal stress inthe direction perpendicular to extrusion is 48 MPa and the elongation inthe direction perpendicular to extrusion is 950%.

The film is characterized by an impact resistance of 0.9 g/μm.

The film also is characterized by a resistance to tear propagation of0.7 N in the direction of extrusion and 0.95 N in the directionperpendicular to extrusion.

EXAMPLE 4 (COMPARATIVE)

Example 3 was repeated in the absence of DHBP.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 5 (symbol +).

The variation in dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 6(symbol +).

It was not possible to obtain a film by blowing extrusion from thecomposition according to example 4.

The ratio between the speed of crystallization of the compositionaccording to the invention (example 3) and the speed of crystallizationof the corresponding composition (comparative example 4) is equal to3.45.

The ratio between the induction time of the composition according to theinvention (example 3) and the induction time of the correspondingcomposition (comparison example 4) is equal to 0.65.

EXAMPLE 5

Example 3 was repeated, adding 30% by weight, in relation to the finalcomposition, of OMYA BLH™ calcium carbonate and 3.5 g of the stabilizingagent IRGANOX® 1330 per kg of poly-_(ε)-caprolactone.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 7 (symbol _(Δ)).

The variation in dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 8(symbol _(Δ)).

A film (No. 5.1) was prepared starting from the composition according toexample 5 in the manner described hereinabove and with the conditionsset forth hereinbelow.

Flow rate Speed, Drawing Inflation Film No. kg/h m/minimum Thicknessrate rate 5.1 3 1.4 50 2.4 4.6 Film No. 5.1 is characterized by animpact resistance lower than 0.8 g/μm.

EXAMPLE 6 (COMPARATIVE)

Example 5 was repeated in the absence of DHBP.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 7 (symbol _(•)).

The variation in dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 8(symbol _(•)).

It was not possible to obtain a film by blowing extrusion from thecomposition according to example 6.

EXAMPLE 7

A mixture of 40% by weight of CAPA® 680 poly-_(ε)-caprolactone and 60%by weight of CAPA® 650 poly-_(ε)-caprolactone was introduced into theloading zone of the WERNER & PFLEIDERER ZSK® 58 extruder and was spreadthrough the different zones of the extruder.

In the loading zone of the extruder there also was introduced DHBP inthe form of a mixture of DHBP-45-IC with CAPA® 65100poly-_(ε)-caprolactone as described hereinbefore. The total flow rate ofthe poly-_(ε)-caprolactones is 150 kg/h and the quantity of DHBP is 1g/kg of the mixture of poly-_(ε)-caprolactones.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ on the compositionobtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 9 (symbol _(▪)).

The variation in the dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 10(symbol _(▪)).

A film was prepared starting from the composition according to example 7in the manner described hereinabove and with conditions similar to thoseused for the film prepared starting from the composition according toexample 3.

The film obtained is characterized by a homogeneous thickness and bycharacteristics similar to the one obtained starting from thecomposition according to example 3.

EXAMPLE 8 (COMPARATIVE)

Example 7 was repeated in the absence of DHBP.

The values for RMFI, gel level, mean molecular mass in number,crystallization temperature (T_(c)) and tan δ measured on thecomposition obtained are set forth in Table I.

The variation in elongational viscosity (expressed in kPa.s) at 80° C.,according to time (expressed in s) for an elongation gradient (expressedin s⁻¹) of 1 is illustrated in FIG. 9 (symbol _(▾)).

The variation is dynamic viscosity (expressed in Pa.s) according tofrequency (expressed in rad/s) at 80° C. is illustrated in FIG. 10(symbol _(▾)).

It was not possible to obtain a film by blowing extrusion from thecomposition according to example 8.

TABLE I Gel level Mean molecular T_(c) Example RMFI (%) mass in number(° C.) Tan δ 1 1.31 0 80,000 35 1.15 2 comparative 0.96 0 70,000 32 8.183 1.61 0 64,000 36 1.64 4 comparative 0.90 0 55,000 32 27.2 5 1.31 064,000 36 1.62 6 comparative 0.98 0 55,000 35 37.9 7 1.7  0 59,000 341.47 8 comparative 0.90 0 55,000 32 27.2

From the analysis of the results of Table I, it appears that thecompositions according to the invention are characterized by acrystallization temperature (T_(c)) which is at least 1° C. higher thanthose observed for the corresponding compositions. In addition, it isnoted that the crystallization speed of the compositions according tothe invention is much greater than that of the correspondingcompositions.

The compositions according to the invention furthermore arecharacterized by a tan δ value clearly lower than those measured for thecorresponding compositions.

From the study of FIGS. 3, 5, 7 and 9, it appears that the compositionsaccording to the invention furthermore are characterized by anexponential increase in elongational viscosity according to time,characteristic of a structural hardening under stress, unlike thecorresponding compositions.

In addition, the point of inflection corresponding to the exponentialincrease in elongational viscosity according to time is less than 3seconds, unlike the corresponding compositions.

From the study of FIGS. 4, 6, 8 and 10 (logarithmic graphs) it appearsthat the compositions according to the invention furthermore arecharacterized by a nearly linear relationship between dynamic viscosityand frequency. As for the corresponding compositions, they arecharacterized by an evolution of dynamic viscosity toward the descendingfrequencies in the form of a Newtonian plateau.

From the study of the results relating to the films obtained, it appearsthat the compositions according to the invention make it possible toobtain films. These films are resistant to traction, impact and tearing.On the other hand, the corresponding compositions do not make itpossible to obtain films by blowing extrusion.

What is claimed is:
 1. A process for preparation of a thermoplasticpolyester composition, comprising: passing a thermoplastic aliphaticpolyester into an extruder successively comprising a polymer loadingzone, a melting zone, a homogenization zone, a reaction zone in whichmolten thermoplastic aliphatic polyester reacts with a radical generatoremployed in a quantity ranging from 0.01 to 0.2% by wt based on thethermoplastic aliphatic polyester, and a discharge zone, wherein thetemperature of the loading zone is ≦20° C., the temperature in themelting zone and in the homogenization zone is ≧ the melting temperatureof the polymer and ≦ the temperature at which the half-life period ofthe radical generator is ten times greater than the dwell time of thematerial in each of said zones and the temperature of the reaction zoneis ≧ the temperature at which the half-life period of the radicalgenerator is ≦the dwell time of the material in this zone, therebyproducing an extrudate having an RMFI value ranging from 1.1 to 2.5; andobtaining the extruded polyester.
 2. The process according to claim 1,wherein the aliphatic polyester entering the extruder is such that theester functions thereof are separated by a chain of at least 2 carbonatoms.
 3. The process according to claim 1, wherein the extruder devicefurther successively comprises an additive introduction zone and adegassing zone after the reaction zone.
 4. The process according toclaim 1, wherein the radical generator is introduced into the extruderin a mixture with carbon dioxide.
 5. The process according to claim 1,wherein the radical generator is introduced into the extruder by meansof a thermoplastic aliphatic polyester that contains a radicalgenerator.
 6. The process according to claim 1, wherein the radicalgenerator is introduced into the extruder by means of a filler materialcontaining the radical generator.
 7. The process according to claim 6,wherein at least one filler material is incorporated into thethermoplastic aliphatic polyester by introduction into the extruder. 8.The process according to claim 1, wherein the aliphatic polyester thatis produced has a dynamic viscosity, as measured at a temperature 20 to40° C. higher than the melting temperature of the thermoplasticaliphatic polyester, ranges from 0.1 to 100 rad/s.
 9. The processaccording to claim 1, wherein the aliphatic polyester is ahydroxyalcanoate, polybutylene succinate or a ε-caprolactone polymer.10. The process according to claim 9, wherein the ε-caprolactone polymeris a copolymer having a ε-caprolactone content of at least 50% by weightwith a comonomer selected from the group consisting of β-propiolactone,γ-butyrolactone, δ-valerolactone, 1,4-dioxane-2-one,1,4-dioxepane-2-one, 1,5-dioxepane-2-one and a glycolide.
 11. Theprocess according to claim 1, wherein the thermoplastic aliphaticpolyester is comprised of a mixture of 0.1 to 80% by wt of a lowmolecular weight polyester component and 99.9 to 20% by weight of a highmolecular weight polyester component.
 12. The process according to claim11, wherein the low molecular weight aliphatic polyester has a numberaverage molecular weight ranging from ≧10,000 g/mole to ≦60,000 g/moleand the high molecular weight aliphatic polyester has a number averagemolecular weight ranging from ≧60,000 g/mole to ≦200,000 g/mole.
 13. Theprocess according to claim 1, wherein the aliphatic polyester has anRMFI value ranging from 1.2 to 2.